Maybe its wiser to do a full reinstall, its radical but i think its the best way.
First: save your c:\maniaplanet\skins folder on another place so you can replace it after the reinstallation. (if you are using your own skin /avatar)
Deinstall the current maniaplanet in your controlpanel of windows.
Then got to
http://player.maniaplanet.com/
Login there with your maniaplanetusername and pass.
Then go to
https://player.maniaplanet.com/account/downloads and download there the
Maniaplanetminimal setsup.exe
After downloading, all nescessary updates will follow automatically. After installing Maniaplanet go to the store and install the Trackmania2 title. If you install this first it will automatically install all 3 titles. Then you dont have to swap from title to title during installing. If that doesnt work you can install it also of course title by title.
Dont forget to replace your old skins folder!!
Good luck!